1. Field of the Invention
The present invention relates to materials and devices for optical communications, and more particularly to electro-optic ceramic materials having high transparency and electro-optic activity and devices constructed using such materials.
2. Technical Background
While much progress has been made in the last thirty years in developing optical switches or modulators, current devices are not satisfactory for every application. Many active optical devices, such as intensity attenuators, used in present-day systems are based on electromechanical actuation. In one type of conventional device, optical fibers are positioned end to end and mechanically moved into or out of line. In another type of conventional device, mirrors are rotated to direct beams into or away from a receiving fiber. This can be accomplished mechanically, or with piezoelectric or electrostatic devices. Devices based on motion of components have slow switching times, and may have unacceptable environmental or long-term stability.
Optical devices without moving parts have been designed to address some of the switching speed and stability problems mentioned above. These devices depend on materials that can change optical properties without bulk motion, such as liquid crystals and electro-optic crystal materials. Liquid crystals tend to have relatively slow switching speeds, as the mechanism of actuation is rotation of entire molecules under the influence of an electric field. Electro-optic crystal materials such as LiNbO3 have much higher switching speeds, but are extremely polarization dependent.
One especially promising class of materials for use in active optical devices is electro-optic ceramic materials. Electro-optic ceramic materials are generally composed of ferroelectric complex oxides, and are polycrystalline. Due to the random orientations of the individual crystalline grains, electro-optic ceramic materials are optically isotropic in the absence of an electric field. In the presence of an electric field, electro-optic ceramic materials become anisotropic, with a lower refractive index in the direction of the field than perpendicular to the field. These materials may be switched between isotropic and anisotropic states by controlling the electric field. For use in electro-optic applications, it is desirable that electro-optic ceramic materials have high transparency, high quadratic electro-optic coefficients and low switching hysteresis.
Lead lanthanum zirconate titanate (PLZT) is the most common electro-optic ceramic material. PLZT materials can be formed to be substantially transparent to light having wavelengths in the range of 0.5 xcexcm to 7 xcexcm. Properties of PLZT compositions can be tuned by adjusting the relative amounts of lead, lanthanum, zirconate and titanate. For example, a PLZT composition having the formula Pb0.91La0.9(Zr0.65Ti0.35)0.9775O3 has a quadratic electro-optic coefficient R=9.2xc3x9710xe2x88x9216 m2/V2, but has extremely high hysteresis in its switching behavior as well as poor temperature stability, making it unsuitable for high-speed electro-optic applications. By increasing the lanthanum concentration, one can improve hysteresis at the expense of electro-optic activity. For example, a PLZT composition having the formula Pb0.9025La0.0975(Zr0.65Ti0.35)0.975625O3 has a lower quadratic electro-optic coefficient (Rxcx9c2.5xc3x9710xe2x88x926 m2/V2 at room temperature), but has temperature stability and hysteresis suitable for use in devices for optical telecommunications. PLZT materials also suffer from high brittleness and low toughness. Attempts to find new electro-optic ceramics have generally failed to provide an electro-optic ceramic material that has high transparency, a high quadratic electro-optic coefficient, and low hysteresis.
One embodiment of the present invention relates to an electro-optic ceramic material including lead, zinc and niobium, wherein the electro-optic material has a propagation loss of less than about 3 dB/cm and a quadratic electro-optic coefficient of greater than about 1xc3x9710xe2x88x9216 m2 V2 at 20xc2x0 C. at a wavelength of 1550 nm.
Another embodiment of the present invention relates to an electro-optic ceramic material including lead, zinc and niobium, wherein the electro-optic material has a propagation loss of less than about 3 dB/cm and a quadratic electro-optic coefficient of greater than about 1xc3x9710xe2x88x926 m2 V2 at 20xc2x0 C. at a wavelength of 1550 nm, and wherein the electro-optic ceramic material further includes titanium, wherein the electro-optic ceramic material has a lead cation fraction of between about 0.20 and about 0.50; a barium cation fraction of less than about 0.26; a lanthanum cation fraction of less than about 0.05; a zinc cation fraction of between about 0.07 and about 0.17; a niobium cation fraction of between about 0.15 and about 0.33; and a titanium cation fraction of between about 0.03 and about 0.27.
Another embodiment of the present invention relates to an electro-optic ceramic material including lead, zinc and niobium, wherein the electro-optic material has a propagation loss of less than about 3 dB/cm and a quadratic electro-optic coefficient of greater than about 1xc3x9710xe2x88x9216 m2/V2 at 20xc2x0 C. at a wavelength of 1550 nm, and wherein the electro-optic ceramic material has the formula Pb1xe2x88x92yxe2x88x92zBayLaz[(ZntNb1xe2x88x92t)xTi1xe2x88x92x]1xe2x88x92z/4O3+x/2xe2x88x923xt/2xe2x88x92xz/8+3+xtz/8, wherein x is between about 0.5 and about 0.9, y is between about 0.05 and about 0.5, z is between about 0 and about 0.05, and t is between about 0.30 and about 0.36.
Another embodiment of the present invention relates to an electro-optic device including an electro-optic ceramic material including lead, zinc and niobium, wherein the electro-optic ceramic material has a propagation loss of less than about 3 dB/cm and a quadratic electro-optic coefficient of greater than about 1xc3x9710xe2x88x926 m2/V2 at 20xc2x0 C. a wavelength of 1550 nm.
Another embodiment of the present invention relates to an electro-optic device including an electro-optic ceramic material including lead, zinc and niobium, wherein the electro-optic ceramic material has a propagation loss of less than about 3 dB/cm and a quadratic electro-optic coefficient of greater than about 1xc3x9710xe2x88x926 m2/V2 at 20xc2x0 C. at a wavelength of 1550 nm, wherein the electro-optic ceramic material further comprises titanium, and wherein the electro-optic ceramic material has a lead cation fraction of between about 0.20 and about 0.50; a barium cation fraction of less than about 0.26; a lanthanum cation fraction of less than about 0.05; a zinc cation fraction of between about 0.07 and about 0.17; a niobium cation fraction of between about 0.15 and about 0.33; and a titanium cation fraction of between about 0.03 and about 0.27.
The materials and devices of the present invention result in a number of advantages over conventional materials and devices. The materials of the present invention have high transparency over a wide wavelength range as well as high quadratic electro-optic coefficients. The materials of the present invention require a lower temperature for fabrication than does PLZT. The materials of the present invention have low hysteresis, making them suitable for use in electro-optic devices for telecommunications applications. Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the invention as described in the written description and claims hereof, as well as in the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings are not necessarily to scale. The drawings illustrate one or more embodiment(s) of the invention, and together with the description serve to explain the principles and operation of the invention.